There has been some discussion in recent
times regarding whether or not substorm expansive phase activity plays any role
of importance in the formation of the stormtime ring current. I explore this
question using the Kp index as a proxy for substorm expansive phase
activity and the Dst index as a proxy for symmetric ring current
strength. I find that increases in Dst are mildly related to the strength
of substorm expansive phase activity during the development of the storm main
phase. More surprisingly, I find that the strength of Dst during the
storm recovery phase is positively correlated with the strength of substorm
expansive phase activity. This result has an important bearing on the question
of how much the Dst index reflects activity other than that of the
stormtime symmetric ring current strength for which it is supposed to be a
proxy.